We presented the first clinical images generated with compact, clinical-adapted FFOCT. This was made possible thanks to the replacement of the former Adaptive Lens by a Woofer-Tweeter approach, combining a Variable Focal Lens for defocus correction, and the Phaseform’s Deformable Phase Plate for high-order aberrations correction, enabling to improve both SNR and lateral resolution when imaging patients.
A simulation tool has been developed for the evaluation of Deformable Phase Plate (DPP) in optical systems. The tool, in the form of a dynamic-link library (DLL), predicts the behavior of a DPP by incorporating its empirically measured characteristics.
Microscopy through inhomogeneous media distorts the wavefront of the transmitted light and results in the loss of resolution and contrast. This wavefront distortion may be compensated by the use of adaptive optics (AO). The state-of-the-art AO systems for commercial microscopes generally use deformable mirrors for wavefront modulation, which are difficult to integrate as they require the use of folded imaging paths. Herein, we present a compact and miniaturized AO ’add-on’ that fits between an objective and the turret as a simpler ’plug-and-play’ alternative. The AO add-on features a deformable phase plate - a transmissive, optofluidic wavefront modulator that is capable of wavefront correction up to 7th radial Zernike modes within a clear aperture of 10 mm, and open-loop control based-on sensorless wavefront estimation.
Diffraction-limited imaging in microscopy is only possible if different layers within the objective’s working distance all have an uniform refractive index. However, in many practical imaging problems the samples are inhomogeneous in optical density, and refraction through them introduces field-dependent wavefront aberrations. On the image plane these are manifested in varying degrees of resolution and contrast degradation across the field-of-view. In pupil adaptive optics (AO), where a wavefront modulator is accommodated at the objective’s pupil-plane, a single correction profile is applied for all fields, and the correctable field-of-view (FoV) is limited by the isoplanatic patch. In the alternative configuration of conjugate adaptive optics, where the corrective element and the dominant aberrating layer within the sample sit at optically conjugate planes, effective correction across the entire FoV is possible in principle. This configuration, however, is relatively difficult to implement with deformable mirrors for wavefront modulation, since several folded optical paths have to be constructed. In this work, we present the design and evaluation of a completely in-line conjugate-AO system based on a refractive wavefront modulator (DELTA7 from Phaseform GmbH, Germany). We evaluate the performance of the system on a Zeiss Axiovert inverted microscope by imaging fluorescent beads through custom-fabricated phase plates.
A 63-electrode optofluidic refractive wavefront modulator enabling spatial frequency correction up to the seventh radial Zernike order, the highest spatial order ever achieved with a refractive dynamic wavefront modulator, is presented. The modulator is designed so that aberration correction performance is nearly identical in both horizontal and vertical orientations, virtually eliminating the gravity-induced parasitic surface deformations typical for optofluidic devices. With 55 of its electrodes located within the 1-cm clear pupil, the modulator offers the versatility of continuous face-sheet deformable mirrors within a compact, high efficiency, and transmissive device. Using a fluidic interfacing method based on wafer-level 3D micro-structuring of glass, the modulator is only 0.86-mm-thick, facilitating the cascading of multiple modulators within close proximity. We demonstrate a bi-directional stroke of more than 13 λ, and replications of Zernike mode shapes up to the seventh radial order with high fidelity, representing a significant leap in the performance of ultra-miniaturized refractive wavefront modulators.
We report a new optofluidic transmissive wavefront modulator optimized for gravity-neutral performance and miniaturized dimensions. The modulator is optimized for compensating gravity-induced aberrations by simulating its behavior with various design configurations. Miniaturization was achieved by a novel method for liquid filling and sealing of the modulator. Key elements of the new interface are intra-substrate channels fabricated by a selective laser-induced etching process. The modulator has a final thickness of 750 µm and can be operated in any orientation without significant loss of modulation quality.
We discuss the implementation and performance of an adaptive optics (AO) system that uses two cascaded deformable phase plates (DPPs), which are transparent optofluidic phase modulators, mimicking the common woofer/tweeter-type astronomical AO systems. One of the DPPs has 25 electrodes forming a keystone pattern best suited for the correction of low-order and radially symmetric modes; the second device has 37 hexagonally packed electrodes better suited for high-order correction. We also present simulation results and experimental validation for a new open-loop control strategy enabling simultaneous control of both DPPs, which ensures optimum correction for both large-amplitude low-order, and complex combinations of low- and high-order aberrations. The resulting system can reproduce Zernike modes up to the sixth radial order with stroke and fidelity up to twice better than what is attainable with either of the DPPs individually. The performance of the new AO configuration is also verified in a custom-developed fluorescence microscope with sensorless aberration correction.
When imaging a sample, inhomogeneities in refractive index cause blur in the image and decrease resolution. Adaptive optics (AO) is a technique that can correct for the resulting aberrations. The most common implementation of AO uses a single deformable mirror that is conjugate to the pupil. A single pupil-conjugate corrective device provides correction over a limited field of view owing to field-dependent aberrations. To overcome this limitation, an additional specimen-conjugate deformable mirror can be used. However, adding a second reflective correction device significantly increases system complexity. We have developed a closed-loop multiconjugate AO system for field-dependent aberration correction in a confocal fluorescence microscope. A 140-actuator deformable mirror is used in the pupil plane with a custom 37-element transmissive deformable phase plate inserted in a sample-conjugate plane. Both devices are calibrated and controlled in closed-loop using a Shack-Hartmann sensor in combination with an integral control law. The sensor consists of an EMCCD and lenslet array with a 500 μm pitch and a 47 mm focal length. Results from a Drosophila ovary and HeLa cells are presented.
Two-dimensional spatial wavefront modulation in real-time is an essential tool for applications such as adaptive optics and laser beam shaping. Micro-mirror-based MEMS wavefront modulators have led to a major reduction in the cost of practical wavefront modulation, but the system complexities due to their reflective operation are still prohibitive. To address this issue, we demonstrate here a highly-miniaturized electrostatically actuated optofluidic transmissive phase modulator capable of positive or negative phase shifting through the use of hydromechanical coupling. The approach is based on a unique push-pull electrostatic actuation concept that exploits the inherent liquid-mechanical coupling in the design and is free of polarization and diffraction effects. This optofluidic phase modulator is able to correct aberrations up to 5th radial Zernike polynomial modes with high fidelity and, by use of sensorless wavefront estimation algorithms, allows for the realization of a completely in-line adaptive optics system.
We introduce an optimization-based open-loop control method for 2D wavefront modulators. The optimization problem is convex with inequality constraints and can be solved using an interior-point method in real-time. Compared to conventional influence matrix inversion, this new method takes into account the system limitations, such as the actuation polarity and voltage limits of the drivers. It searches for the global optimum of actuation signals within system boundary constraints. Consequently, while reducing the complexity of the hardware, it is more immune to systematic errors and guarantees optimality of the actuation signals. The control system is implemented on two different electrostatically-actuated phase modulators; a conventional deformable mirror and a novel refractive optofluidic phase modulator. We experimentally compare the performance of the optimizationbased controller with conventional methods for high order Zernike mode replication. It is demonstrated that the introduced technique enables more accurate control for both modulators, particularly at large correction amplitude and/or higher order corrections.
A low-cost, compact electrostatic deformable mirror is developed using widely available polymeric materials. The fabrication method offers exceptional post-fabrication mirror flatness error of < 250 nm RMS, which can be reduced below 22 nm at best-flat. A custom real-time control system is also constructed and high fidelity reconstruction of Zernike modes up to the 4th radial order is presented. Real-time wavefront correction is also demonstrated using a spatial-carrier laser interferometer as a wavefront sensor.
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